1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device and, more particularly, to a method of manufacturing a semiconductor device, capable of micropatterning a ruthenium oxide and ruthenium.
2. Description of the Prior Art
In recent years, the research and development of microelectronics devices (e.g., a dynamic random access memory (DRAM)) using a typical conductive oxide (RuO.sub.2, IrO.sub.2, OsO.sub.2, or RhO.sub.2) having a rutile structure have advanced. In the manufacture of such microdevices, the developments of film formation techniques for conductive oxides and process techniques such as micropatterning for forming devices are indispensable.
A technique for micropatterning RuO.sub.2 of the conductive oxides utilizing plasma etching using an oxygen gas plasma (e.g., U.S. Pat. No. 5,254,217 (Oct. 19, 1993) and reactive ion etching using tetrafluoromethane (CF.sub.4) gas added to oxygen (e.g., "Plasma Etching of RuO.sub.2 Thin Films", Jpn. J. Appl. Phys. vol. 31, (1992), pp. 135-138) are known. In the plasma etching using an oxygen gas plasma, the pressure was kept at 45 mTorr, the oxygen flow rate was set to 50 sccm, and the 13.56-MHz, 200-W RF power was supplied (at this time, a DC bias generated in a lower electrode was 516 V). The etching rate was 57 .ANG./min. In the reactive ion etching using the CF.sub.4 gas added to oxygen, the pressure was kept at 40 mTorr, the 13.56-MHz, 150-W power was supplied, and the total gas flow rate was 30 sccm. The etching rate of 50 to 100 .ANG./min was obtained in the range of 0 to 50% of CF.sub.4.
In an RuO.sub.2 micropatterning process of a conventional method of manufacturing a semiconductor device, when plasma etching using an oxygen gas plasma is employed or even when reactive ion etching using CF.sub.4 added to oxygen is employed, the etching rate is a maximum of 100 .ANG./min or less. Satisfactory productivity cannot be obtained in the manufacture of semiconductor devices containing ruthenium oxides and ruthenium. An etching mask material (e.g., a resist, and a so-called hard mask such as a silicon oxide film, a silicon nitride film, and any other metal material) is etched at an etching rate equal to or higher than that of RuO.sub.2 in reactive ion etching or physical sputtering. An etching ratio of RuO.sub.2 to a mask material, i.e., a selectivity ratio may be expected to be as low as x1.